The subject matter disclosed herein relates generally to systems and methods for the detection of ionizing radiation, such as gamma-ray and X-ray radiation, and more specifically to scanning systems and methods of radiation detection for medical diagnosis including Single Photon Counting Tomography (SPECT).
Different scanning methods are known for use in detecting ionizing radiations, such as systems that use variable collimators. For example, some known methods of three dimensional (3D) image reconstruction use multiple image-acquisitions with different collimations of the imaging-collimator, such as by changing the collimation of the imaging-collimator. These systems use forward looking variable collimators constructed from multiple collimation elements where each collimation element may be varied and may produce multiple corresponding viewing-angles with a primary axis that is normal to imaging planes produced by detectors. These imaging planes are behind the collimators and arranged to receive the radiation emitted from an imaged object via the collimators. The structures of the collimators and collimation elements are designed to reduce or avoid any crosstalk of radiation between the collimation elements, for example, to prevent or reduce the likelihood of gamma rays passing through the gap of one septum into another collimator aperture.
Additionally, the different viewing angles produced by the variable collimation elements are included in each other in a way that each viewing angle contains all the viewing angles that are smaller than this viewing angle. As a result, acquisition of multiple images using variable collimators using conventional systems creates a significant redundancy of information in which the same information appearing in one image appears in another images as well. In some of the images, the repeated information is the major information and only a small fraction in these images is new information that does not appear in other images.
In order to increase the sensitivity of the imaging system, each of the multiple images acquired in different collimation of the imaging-collimator includes the imaged region. This imaged region is on and in the imaged object and is significantly larger than the size of the desired spatial resolution. The reconstruction of the image within the desired spatial resolution is produced by various image-reconstruction methods which include intensive mathematical calculations based on multiple equations derived from the multiple images. For example, in some systems, the number of images acquired for reconstructing a SPECT image times the number of pixels in each image is equal to the number of virtual voxels into which the imaged object is to be divided. Accordingly, the large size of the imaged region, on the imaged object, in each acquired image and the large number of acquired images that is needed for the 3D image reconstruction does not allow for selecting only images acquired with no information redundancy.
Moreover, the redundancy of the acquired information increases the statistical error in the equations that contain the repeated information without adding new information useful for the image reconstruction. Also, the equations in which the repeated information is significant are dependent equations and do not contribute insignificant information for the image reconstruction. The redundant or repeated information in general and especially the redundant or repeated information in the dependent equations, contribute mainly statistical errors without any substantial new information. These statistical errors are enhanced by the intensive mathematical calculations involved in the image-reconstruction methods.
Thus, the reconstruction of images using some known systems and methods includes repetitive information that enhances the statistical errors when using the algorithm for image reconstruction. Thus, reconstructed images may suffer from poor quality and may also include reconstruction artifacts.